Storage amplifier circuit



Jufiy H6, 1946. K. SCHLESINGER 2,403,956.

STORAGE AMPLIFIER CIRCUIT Filed May 11, 1945 6 Sheets-Sheet l 1/ 7 l: 47 I a 3- 5 i I e /'f I Lt I my {f :ELA? I I II, I i: i 0 g? ii 5 3L- Ig35 4/ i /6 l 1 v 23. L J

INVENTOR.

1 I BY H 4 ATTOPNEL July 16, 1946. K. SCHLESINGER 2,403,955

STORAGE AMPLIFIER CIRCUIT Filed May 11, 1943 I 6 Sheets-Sheet 2 F MQ.

INVEIYTOR.

Kart paws A TTOPNEY July 16, 1946. K. SCHLESINGER STORAGE AMPLIFIER CIRCUIT Filed May 11, 1945 6 Sheets-Sheet 3 WQTER LINE WH TEX L INE PEflCH/NG DISTHNGE 6S'EM9/T/ wry) I INIfENTOR.

A TTOPNEL July 16, 1946. K. ST'CHLESINGER 2,403,956

STORAGE AMPLIFIER CIRCUIT Filed May 11, 1945. 6 Sheets-Sheet 4 AAAAAAA lllllllll VIVIII' ""'I"'- inn E Q F b w v g I INVEIYTOR.

ATTOENEV y 16, 1946. K. SCHLESINGER 2,403,956

STORAGE AMPLIFIER CIRCUIT Filed May 11, 1943 6 Sheets-Sheet 5 INIfENTOR.

ATTOPNEY y 1946- K. SCHLESING ER STORAGE AMPLIF]:ER CIRCUIT Filed Ma 11. 1943 6 Sheets-Sheet 6 lllllllll 'I'I'I'II INVFNTOR.

agar

ATTOPNE'K Patented July 16, 1946 STORAGE AMPLIFIER CIRCUIT Kurt Schlesinger, West Lafayette, Ind., assignor to Radio Corporation of America, a corporation of Delaware Application May 11, 1943, Serial No. 486,522

29 Claims.

This invention is related to amplifier apparatus and particularly to amplifier apparatus of a type operating in connection with slowly alternating, quasi-static, electric or magnetic fields in space, and wherein an initial control on the amplifier circuit is exercised by an unbalancing electrical field condition in the region of the apparatus to make possible the detection and/or location of objects or field disturbing conditions. Such action necessitates the use of a phase and amplitude responsive A. C, amplifier system.

The particular invention herein to be disclosed is, generally speaking, related to the substance of co-pending application entitled Electron tube circuit, which was filed on May 11, 1943, as Serial Number 486,521 by this applicant. In the mentioned companion case, the disclosure is directed primarily to an amplifier unit called, for convenience, a "storage amplifier, which may be considered, broadly speaking, to comprise a chain r or cascade of grid controlled rectifier tubes activated from an alternating current source and connected thereto in alternating polarity. The tubes are so arranged as to load suitable energy storage circuit in accordance with the conductive periods of each. As was described in the companion case, whenever the first of the series of grid controlled rectifier tubes becomes operative by having been controlledly energized from some suitable activating source; an electrical energy storage circuit will be charged in its plate and caused to control the second tube during the next half-cycle, and so forth, until sequentially all of the other tubes of the combination repeat and amplify the signal so as finally to produce an observable indication which shall be a retarded, but magnified, indication of the effect initiating the operation.

Further, by the companion case, the operation of the described system was initiated in many of its forms by the unbalancing of an electrostatic field. This eifect initiated the production of observable indications for frequency disturbances Where the frequencies were close to the frequency of the energizing alternating current source. The system heretofore described was also particularly useful and extremely sensitive for providing phase shift measurements between the input and the supply voltage.

The arrangement of the companion case mentioned had reference, at least in part, to a form of protecting signal apparatus wherein an electrostatic field was :built up in the space or area surrounding the location of the storage amplifier unit. The frequency of such alternating field was made to coincide with that of the power supply which was to supply the operating energy to the several grid controlled rectifiers. By suitably arranging the system, a delicately balanced and highly sensitive bridge circuit could be provided to control a suitable indicator unit, and

the system was so set up and constructed that the indicator unit produced a measurement, not only of the presence of the disturbance itself but was an indication of the location and magnitude of the disturbance.

The system to be described in this applica bodies in the vicinity of and up to reasonable distancesaway from the field producing element. The'system of the present invention is designed to provide an indication or recording simultaneously representative of the proximity, as Well as the position, of any object within a 360 angle of the transmitter. a

Since alternating magnetic effects can readily penetrate into water, in contrast to radio waves being reflected from the water surface, and electrostatic efiects not being possible of attainment through water, this invention becomes of particular importance and value in connection with the detection of submarines and sea mines in war time, as Well as for the use and detection of land mines, for instance, or magnetic deposits and for the-protection against collision of various types of transport machines.

many such uses it will be seen, from what is to follow, that there is a commonfeature, generally speaking, of providing ways and means whereby an alternating magnetic field is built up in the space around the station which is equipped with one or more amplifier units of the type hereinabove described, and referred to in more detail in the above mentioned co-pending application. In all cases, the frequency of the alternating field which is developed coincides, as above set forth, with the supply frequency. The result, as will .be explained, is that when any foreign body comes within the produced alternating magnetic field to. change the equilib- I rium of the established field, an'unbalanced conditionin the apparatus results, so that by combining correctional properties of the unit,-the magnitude of the disturbing effect, and also the location thereof, immediately become apparent in indicating apparatus co-ordinated therewith, with each disturbance bein the result of a produced change in the permeability of the field.

Accordingly, it becomes an. object of this in vention toprovide an electronic device capable u i n of operating in such a manner that a slowly alternating, or quasi-magnetostatic field is developed and ferro-magnetic bodies entering that field and disturbing it by their permeability are immediately detected.

A further object of the invention is that of providing a magnetic field which, if disturbed, will react upon a controlled type of storage element to produce therefrom output energy of such magnitude as to give useful indications of the nature of the initiating disturbance.

Other objects of the invention are those of providing an electronic tube circuit which is capable of making measurements of predetermined conditions and reducing those measurements to optical effects, with the magnitude, position or brilliance of such effects being indicative of the nature of the initial disturbance. A further object of the invention is that of providing a protective system readily adaptable for use on ships or the like, whereby searching vessels are able to locate exactly submarines, submerged wrecks and the like, even though the located object remain completely immobile and is well beneath the waters surface.

Other objects of the invention are those of providing a protective system for use in connection with transport media whereby collisions may be avoided and whereby, if the transport medium happens to be a ship, the ship can protect itself from submerged objects by virtue of indications produced in a suitable indicating medium capable of showing the exact location of the object and whether it is stationary or moving.

Other objects and advantages of the invention are to provide a protective system which is relatively simple in its arrangement; a system which will operate at relatively low power, and a system which is highly efficient in its use.

Other objects of the invention will suggest themselves promptly to those skilled in the art to which the invention is directed, when the several forms of circuit and the illustrative explanation, as embodied in the several figures of drawings, is read in connection with the following spec- 4 ifications.

By the drawings:

Fig. 1 illustrates, in schematic form, a simplifled form of magnetic locating device;

Fig. 2 represents a modification of Fig. 1, where the apparatus is utilized in connection with a ship to locate the right or left position relative thereto to a disturbing condition;

Fig. 3 is an explanatory diagram to indicate, generally speaking, the range of operation;

Fig. 4. shows one form of the apparatus as applied to a ship;

Fig. 5 is a modification of Fig. l

Fig. 6 is a further modification wherein a double control system is utilized and response indications for all directions are attained equally as easily;

Fig. 7 is another modification of the arrangement of Fig. 6; and,

Fig. 8 shows a further refinement and simplification of the invention.

In the companion applicatio hereinabove mentioned reference may be made for further details of the specific operation of the storage circuits as a whole. Generally speaking, the circuit of Fig. 1 illustrates broadly the principles upon which operation is based. In the arrangement of Fig. 1, an extremely simple form of the device is illustrated. In this system, the device is so constituted and set up that only the presence III Ill

of some disturbing object within the field can be indicated on the indicating device, rather than the exact position of the disturbance relative to the complete unit.

In the arrangement as it is shown, a disturbing body, such as that shown at IE), is placed within the response range of the storage amplifier unit contained within the shielding area indicated at H. Within the range of the disturbing body l0 there is located a loop I3 which may be orientated horizontally, for instance, as it is shown. To supply energy for developing a magnetic field from the loop i3, alternating current energy power source 15 has been provided. The energy output of this power source is supplied by way of a carefully shielded push-pull transformer ll of the step-down variety to the loop l3, with the shielding indicated at Hi, It is apparent, in this way, that considerable current of relatively low voltage will be fed into the loop is from the source it and, consequently, with the loop constituting a field coil, the field strength which is built up in it, due to the current flowing therein, will have a reaching distance, as will later be shown particularly in connection with Fig. 3, which is directly proportional to its area and to the current or flux produced, but inversely proportional to a power function of the objects distance.

Whenever current fiows through the loop I3, a balanced condition of the bridge circuit formed can be achieved where the variable resistor element i9 is adjusted to compensate for the resistance of the loop and the variable inductance element 2!, which is appropriately shielded, as indicated at 23, is adjusted to compensate for the inductance of the loop l3. The shielding unit 23, at high operating frequencies of the order of 30 kc. should preferably be of copper, whereas at low operating frequencies of the order of cycles, it may be formed of iron and copper. It can be seen that if the secondary winding of the transformer H is split at its center point, which connects to ground 25, as shown, and if the resistance I9 is adjusted to equal the resistance of the loop is, and the inductance 2! is adjusted to equal the loop inductance, a balanced condition for no disturbance within the range or field of the loop I3 may be achieved, with a result that across the diagonal of the bridge between the junction point l8 and ground 25 no energy will flow.

If, now, however. with the inductance 2| carefully shielded, as indicated at 23, a disturbing effect such as a ferro-magnetic body l0 comes within the field of the loop H, a balanced condition no longer will be maintained across the bridge diagonal indicated. Under such circumstances, energy will now flow through the primary winding of the transformer 21 to be supplied, by way of the transformer secondary winding, to the control electrode element of the first tube 29 of the an iplifier unit contained within the shielded area I As was explained in the companion case the same source'of alternating current 15 which energizes the bridge and field coil I3 is connected so as to supply operating voltages to all of the tubes within the unit H with successive tubes being energized by alternate half-cycles of the supply energy source l5. The operating point of the first tube 29 is preferably set by way of the energy which flows through the resistor 3i] and the potentiometer 3!, with the cathode of the tube 29 being connected at some intermediate point on the potentiometer 3|, which results in providing appropriate bias for the complete system.

Whenever a, disturbing condition coming within the field of the loop I3 is such as to unbalance the bridge, it causes current to flow through the input transformer 21. The transformer 21 should be of the step-up variety to provide a voltage increase effect in the secondary winding, at least of the order of 100 to 1, and the transformer should have preferably a core of the type known as permalloy. In this way, the unbalanced conditions will be transferred as alternating voltage waves of the common supply frequency, but of variable phase and amplitude to the control electrode of the tube 29. The unbalance is measured relative to a reference point which; like that of the rest of the system, is established by the ground connection 25 and which might, forinstance, in connection with a ship, be constituted as the metallic body of the ship, or it might, in connection with a tank for instance, where the device is used to search for land mines or to prevent collision, be the tank's armor. The main purpose of the connection is to establish a fixed reference point.

Now, whenever current flows through the transformer 21 to produce an activating or control signal voltage on the control electrode of the tube 29, that tube will draw current from source l5 during half-cycle periods when positive voltage is applied to its plate or anode. The magnitude of this half-wave pulse of plate current in the tube 29 will depend entirely upon the phase and amplitude, during that cycle, of the unbalance of the bridge system transferred to the grid from the step-up input transformer 27. It thus can be appreciated that whenever current flows through the tube 29, it causes an electrostatic charge to be built up in the condenser element of the storage circuit 33, which includes also the plate resistor 31 of the tube 29. The magnitude of the charge in the condenser 35 is made proportional to the disturbance efiect upon-the loop l3 which initiated the current flow in the tube 29.

During the next half-cycle of the power supply l5, the tube 39 (assumed to be the second tube of the series) will commence to draw current. The average bias on the tube 39, like other tubes of the system, has been automatically set by that bias applied to tube 29, as was explained in more detail in the companion case hereinabove mentioned. The current flow through tube 39 will be measured by, and determined in accordance with, the energy charge in the storage circuit 33. In a manner like that explained for tube 29, current flowing through the tube 39 will cause energy to be stored in its associated storage circuit 4|. This energy may then be transferred through a suitable number of additional amplification stages, operating in a similar manner and connected through conductor 43, for instance, until the output tube of the sequence finally receives the signal. In this last or output tube of the sequence, the output energy is caused to produce an indication on the indicating device or meter 41 where the resultant indication is a measure of the magnitude of the disturbance only, but not indicating the direction from which the disturbance originated. As an example, if the indicator 41 indicates a zero reading for an equilibrium condition, the presence of a disturbing body l9 within the effective field of the loop l3inaybe made to cause always a positive indication on the indicator 41, with the magnitude of the indication proach., The indication is, however, dependent upon the angle under which the disturbanceap pears, ,as seenfrom theloop. It is a cos law with'respect to the loop axis, with the maximum sensitivity along theaxis. W In themodification of F 2, itbecomes pos sibleto-make a frightorleft indication, in addi-, tion; to information about the proximity of; the disturbance." Y Y To this end, in Fig. 2, two field coils l3 and I3 are providedand arranged in parallel j vertical planes on each side of a metallic ship (that is, for instance,-starboard and port) and each coil is energized from the same source I 5 in a balanced-to-ground manner. As the figure is drawn, the, ship is being viewed, for instance,

from a position almost directly over it butslightly to one side, so that the coils or loops: l3 and I3 may be considered as being supported on the sides of the vessel.

order to provide energy to the coils or loops l3 or l3, a generator unit I5 is again provided. This generator supplies alternating current to the loops in phase opposition and, by virtue of an unbalanced condition occurring when ferro-magneticobjects'come within the reachin distance of the loops, indications will'be producedon an indicating element 41," in accordance with the general method described in connection with Fig. 1.

It will be understood,in connection with .an 7

arrangement'of the type of Fig. 2, that the vessel H forms a ferro-magnetic shell to which the ground point 25 may be made. This is quite essential as it. makes the two field coils I 3, l3 virtually independent of each other. The energy output'of the generator I 5 which, in the example illustrated, may be alternating current developed at a frequency of the order of 20 kc., is connected to energize simultaneously the various grid controlled'rectifier tubes 29, 39, and so on, to the output tube 45 in a manner already explained.

In order that strong currents may be set up and caused to flow through the coils l3 and I3, anti resonance is introduced by suitable condenser units 49 and 59, which are connected'intermediate these coils or loops and the power source l5. These condensers, when serially connected, provide tuning at a frequency of the enerator which makes possible the developr'rintof high currents in the loop at relatively small power of the generator. The indicating element d'lof the circuit of Fig. 2 is adjusted by application of cathode bias into the first tube at 3!, as above mentioned. The bridge arrangement, on the. a

other hand, is so adjusted thatthe point It from which energy is derived carries no voltage with respect to ground in the balanced condition. This bridge-adjustmentmay be brought about by suitabletapping of the generator winding I5 at l3, and/or by individual tuning of the two field coils or bridge arms 49, 59, as shown in Fig. 2,

at their respective condensersf The step-up transformer 21 is illustrated in the arrangement of Fig. 2 in the form of the so-called auto-transformer, which is well known, and provides voltage step-up between the loops l3 or l3 and the input circuit of the tube 29, which of the several tubes of the series.

Under conditions of normal balance, as outlined, it will be'seen that wheri'any disturbing body comes within the range of the electro-magnetic fieldset up by the coils or.

constitutes the first loops l3 or I3,

an unbalanced or input voltage will be set up to be applied to the first tube 29 of the amplifier unit. This voltage will be in phase with or in phase opposition to the voltage of generator l5, dependin upon whether the disturbing effect becomes effective first upon the loop l3 or upon the loop l3. Whatever disturbing voltages are induced by such operation to apply control voltage to the first tube will, in the manner already explained, produce an increase or decrease in'the output current flowing from the output tube 45, and in this way a resultant indication will appear upon the indicator 4'! by an indication of the pointer to the right or left, for instance.

To establish the range or distance within which a system of the type above described shall be effective, general reference may be made to the showing of Fig. 3. In this arrangement, the loop 13, which may be assumed to be arranged according to the forms previously described, or in accordance with forms later to be described herein, may be assumed to be energized by a current I. The loop, for purposes of present consideration, will be assumed to have n turns about an area A. Generally speaking, there will be only a single turn of the loop so that the term n may be neglected under most conditions. In any case, it will be appreciated that the coil 13 may be assumed to be duplicated by a magnetic dipole having a dipole moment Do as shown, where D=1LIA (1) This dipole will produce a magnetic field H1 at the location of the intruder, which may be expressed by the equation H1: 2D :3cos a (2) where the angle 0. represents the angle at which the intruder or disturbing body 60 is assumed to be positioned relative to the dipole (see Fig. 3) and ,r indicates the distance.

For purposes of these considerations, .the disturbing body or intruder may be assumed as a ferro-magnetic body 68 with practically infinite permeability and a volume which can be represented V1. Under these circumstances, the originally produced field will build up a magnetization of the body 60 which may be duplicated by the following induced dipole moment 4 cos aV H2 D0. .5 Consequently, the reflected magnetic flux is:

2 =AH cos a= 3 --V A 1LI Thi reflecting field will induce a countervoltage in the coil and cause an unbalance of the bridge, as above explained, of the following amount:

a 4kAV cos a the foregoing equation, the length factor A may be derived from the self-inductance of the coil after expressing this in the form n A A The equation 6) above may also be written in the following form:

J LAAV cos a 1': A

A consideration of the foregoing equation will show that the indicating ability of the disclosed system decreases with the sixth power of the dis tance r and that it depends also upon the azimuth a in the form of a cosine square law (cos as shown by Fig. 3, and it is also proportional to the volume of .the disturbing and intruding body 6% (such as a submarine) as well as the area of the field coil and the sensitivity of the balance indicator of the measuring device. As was above noted, the term it does not appear in the last equation, in that a single turn is considered adequate in most instances, as was above also suggested.

Now, continuing with a consideration of various forms which the system may assume, it will follow, from the analysis above given and with fairly reasonable current and voltages impressed upon the loop 13, that fairly high reaching distances of efiectivenes may be obtained. If only an indication of the presence, but not of the exact location, of an object is required, the arrangement of Fig. 4 illustrates the general form of system, hereinabove explained in connection with Fig. l, with the loop I3 arranged horizontally beneath or around the ship ll and preferably slightly below the water line illustrated. In this arrangement, the ship II is assumed to be formed of ierro-ma'gnetic material in order to make the space inside the ship field-free, so that magnetic bodies may be moved aboard without influencing the system. If the steel hull of the ship is insufficient to bring about magnetic shielding, further improvement may be obtained by a degau'ssing coil inside the hull, energized from the common source, or copper plating may be relied upon.

The bridge, which wa explained in connection with Fig. 1, is again in Fig. i assumed to be completed by the coil 2| and the generator l5, as well as the storage amplifier unit and the stepup transformer 21. The sensitivity of such an arrangement is symmetrical completely around the ship in a horizontal plane, but shows a definite maximum as indicated by the curve of reaching distance or sensitivity. An arrangement of the foregoing type, while having many advantages, such as use in connection with the aiming of depth charges for instance, lacks certain properties of indicating the disturbing bodies in such a way that indication is of maximum usefulness in immediately locating exactly the position of such bodies.

By the arrangement of Fig. 5,, a further improvement in the system is made and the arrangement here disclosed, as in Fig. 2, provides the location of the intruder by means of two loop or field coils 13 and i3 on the two outside and opposite portions of the ship H. The result is that the sensitivity curve indicated by Fig. 5 is improved and the presence of the disturbance on either side of the 'ship is readily indicated in that, if the disturbance is on one side of the ship for instance, one of the field coils, such a I3, will be influenced by its presence, whereas the second field coil I3 is more or less screened from the influence by the ships steel structure. As is apparent from the curve of in-- dication in Fig. 5, the meter or indicator il deflects positive or negative from an intermediate value or equilibrium po ition for disturbances at either the port starboard side; of the ship. Consequently, by reason of symmetry and polarity-opposition, there appears sharp zero indication for an intruder situated directly beneath the ship. This balance is particularly sharp and well defined as it is caused by two strong opposite unbalancing effects cancelling each other rather than by fading or Weak unbalances from distant objects. Therefore, the arrangement of Fig. lends itself particularly well to applications where accurate aiming toward objects just beneath the station is desired, such as depth bombing from submarine destroyers, or slow flying airplanes or helicopters or blimps.

Accordingly, it can be seen that the arrangement of Fig. 4 possesses some advantages not present in Fig. 5, and vice versa.

Now, making reference to Fig. 6, a further modification or" the invention is disclosed where the system provides for locating disturbing fields according to a 369 pattern. To this end, a, rotating field arrangement is provided with four coil elements Mil, I32 and I68, iii i arranged relative to a support element I556 to be energized from a two-phase alternating current source I it. This source feeds its energy by way of conductors H2, IM to energize the transformer H5 and I i 9 by way of supplying energy to primary windings H5 and I29 of these transformers. The energy from the transformer primaries is then supplied to the secondary windings I I! and I 2:, respectively, with the center points H53 of each transformer secondary being connected together and being connected to ground 25, as indicated. Likewise, one terminal of each primary winding I it and I253 is preferably connected to ground 25.

Thus it can be seen, when energy output from the source I It] is supplied to the two transformers H5 and H9, it is fed in one phase to the coils IflI and I02, for instance, and at 90 out-ofphase with respect thereto t the other two coils I93 and HM, respectively.

If new, the two storage amplifier units, generally designated as ldil and we, are connected so that the first tubes 29 and 29' will be controlled by any unbalanced condition, it will be appreciated, in the light of what has heretofore been stated, that the coils or loops NH and I 92 may be connected in bridge fashion so that an unbalanced condition will be represented by the voltage appearing between the point I on the bridge and its diagonally opposite point 25 which represents the ground connection. The bridge arrangement is suitably balanced, as disclosed, in that the windings or coils IilI and 982 on a pair of dipoles are each connected to ground 25, with the point I25 being established as the balance point, so that when a disturbing condition occurs, the control electrode of the first tube 29 is modulated in accordance therewith.

A step-up transformer of the type shown, for instance, at 27, with the circuits of Fig. 1 and Fig. 2, is provided in order that the voltage input may be stepped-up and the control voltage on the first tube shall be adequate. The condensers which are represented in Fig. 2 at 49 and 58 may also be included with the arrangement of Fig. 6,

where desired. The same "energy source III);

which supplies current to'the coils MI nd I02, 7'

I 93IIM, it will be appreciated, from what has been stated above, that a balanced condition or bridge circuit may be established in the same manner, with any unbalanced conditions being represented by a voltage appearing across the bridge diagonal between the point I26 and ground 25. In this way, the unbalanced condition Will produce a control voltage upon the'control electrode of the first tube 29' of the storage amplifier IE3 in a manner like that already explained;

All that is mentioned above about the eastwest system I 92, IIlI with the bridge point I25, holds equally as well for the north' south system I03, I04 with the bridge point H5. Each of the bridge points will exhibit unbalanced voltage, the electrical vector of which will point along the axis of the associated magnetic dipole system in either di-' rection corresponding to the situation or location of the object relative to that dipole system. The twounbalances of the two bridge points I25, I25 are always out-of-phase with respect to each other by in either the positive or negative direction. Both voltages are zero where there are no disturbances and/or in the particular case that th'edisturbance is directly above or directly beneath the quadrupole system, that is, located somewhere alon the axis symmetry normal to the plane comprising the four dipoles I QI-IM. Here again, it will be appreciated that the zero condition just beneath the quadrupole arrange ment Offers extremely accurate indications whereby the device may be used as an accurate bomb sight for depth bombing.

Bias for each of these storage amplifier units It!) and IDS is set by an adjustment of the tapping point on the potentiometers 3| and'3I' to which the cathodes of the first tubes 29 and 29' of the amplifier are connected. The normal adjustment for the output meter reading will be at center-scale if the bridge points are balanced or, which is equivalent, if the input grids are directly short-circuited to groun 25. The storage circuits 33 and 33' are charged, as before stated, in accordance with the current flowing in their associated grid controlled rectifier.

It will be appreciated that the time constant of each of the storage circuits, such as 33, M, and so on, is adjusted so as to be at least of the order of the inverse supply frequency. Under these conditions, the output stage of the final storage amplifier tube shall provide a current impulse of median amplitude which lasts for approximately one h'alfcycle of the supply frequency of the alternating current source II II. The height in magnitude of such an impulse will deviate from some pre-set'normal or median value in the positive or negativedirection according to the position of the disturbing body.

In order to transform these variations of halfwave amplitude of the output of the output tubes 45 and 45' into usable effects to control the defiection in the cathode ray tube, a special control system is provided. It will be seen, from the circuit shown by Fig. 6, that the output energy from the final output tubes 45 and d5 of the storage amplifier units we and I66 is caused to be supplied by way of conductors I36 and I38, respectively, to the deflecting electrode members I3I 11 and I33 of a cathode ray indicating tube I30 in which the electron beam I will be assumed, in the illustration of Fig. 6, to be centrally positioned within the tube. It immediately becomes apparent, from what is disclosed, that if the output energy from the output tubes 45 and 45' varies so that the deflecting plates I3! and I33 are made more positive than their counter-plates I32, I34, respectively, the cathode ray beam will be moved toward these plates. Accordingly, if the beam I60 should move from its central position along a diagonal between the plates I3I and IE3, it might be assumed that some disturbing condition took place between the dipoles IOI and I03 so that this'efiect would be measured as occurring in a direction northwest, for instance, (as indicated by the compass point letters) of the indicator and the magnitude or nearness of the disturbance would become a function of the amount or distance of the lateral motion of the beam I60.

However, in order to provide accurate indications of such effects, it is desirable to compensate for any deflection which might be due to an average or balanced output impulse and, to this end, two diode elements MI and I42 have been provided to connect, by conductors I31 and I39, respectively, to deflecting plate elements I32 and I34, which serve to balance, respectively, any nondisturbance initiated deflection due to a voltage applied to the deflecting plates I3I and I33. To immobilize the spot, the balancing bias at the counter plates I32, I34 has to be a voltage wave itself, rather than a D. C. bias, and this wave must be identical in form, phase and amplitude to the median output wave from the amplifiers in their balanced condition. Such requirements are met by connecting diode rectifiers MI and I42 together with volume controls I43 and I44 across the common plate supply lines H2 and H4.

It will be seen that the diodes are connected in such a way that the plate or anode elements thereof become positive, so that the diode draws current at the same time that the output tubes 45 and 45 of amplifiers I00 and I00 draw current. In this way, it can be appreciated that any deflection of the cathode ray beam I00 in any direction is due to an unbalanced condition of the system, in that the current through the diodes is made independent of the signal appearing upon the input tubes of each storage amplifier, and yet a balanced condition for no disturbing eifect within the field of either of the pairs of dipoles is provided, causing the cathode ray beam I60 to be centrally located for balanced bridges.

If, in the above example, the cathode ray beam I60 should move along a diagonal path between the deflecting plates I3I and I33, it might be assumed that the disturbing body was in the northwest quadrant, and the magnitude of the deflection would indicate the nearness of the body. Thus, if the loop elements or dipoles were installed upon a ship, as above described, the deflection of the beam I60 might indicate the presence and direction of an unseen and submerged submarine. This indication follows all movements of the disturbing body (for instance, the disturbing body might be a submarine) with negligible delay and collapses sharply as soon as the disturbing body is situated directly beneath the ship (for instance, if the disturbing body were a submarine and the ship sailed directly over it) In the modification of Fig. 7, an installation, assumed to be on shipboard, has been illustrated which is closely related to the system described in Fig. 6 but yields a different, and more accurate,

shape of indicator diagram, According to Fig.0, the installation provides for locating ferromagnetic bodies in such a manner as to provide immediate observation of both the direction and the proximity of the disturbance. While the output circuit of Fig. 6, with the compensating diodes included, yields a polar diagram on the cathode ray tube screen in the form of leaflets which broaden in the diagonal directions, the type of circuit shown by Fig. '7 results in a pointer diagram which is equally sharp in all co-ordinates or directions of the compass. In the arrangement provided, the loops IOI, I02 and I03, I06 are provided as before, and these serve to determine the signal control voltage applied to the storage amplifier units, conventionally represented as I00 and I00, respectively.

By virtue of the state of balance obtained, control is had for the trace I00 on the end of the cathode ray tube I55 and various patterns, de-

, pending upon conditions, are traced and more specifically described in the mentioned companion case. As was before indicated, the two pairs of coils are arranged externally to the magnetic shielded body I06 with the axes of the coils being at one to the other. The two-phase generator or A. C. source I I0 is connected, as before, to energize the two pairs of coils with current 90 outof-phase, so that a rotating field is built up externally of the shielded space I00. The frequency of the alternating current generated by the twophase generator IIO may, for general purposes, be of the order of 10 kc. or more, which makes possible the tuning of the coils or loops shown by way of the reasonably small condensers 50 and 50' for the loops IOI and I02, while the condensers 49 and 49 provide adequate tuning for the loops I03 and I04. Thus, greatly increased currents and more powerful fields are set up by resonance phenomena, with comparatively small power at generator I I0.

In order that the magnetic bridge may be provided in each of two directions, the generator I I0 has its center tap connected to ground 25, as indicated. While the generator IIII may be a high frequency alternator, in the order of 1 kw. or more, an ordinary vacuum tube generator may be used equally as well as a dynamo, and readily can develop the necessary power. Such a tube transmitter preferably would comprise a common master oscillator serving to energize the grid circuits of two output stages So that two pairs of push-pull power stages, each of approximately one-half kilowatt or more, may be provided for the two pairs of field coils, with one of the units driven through a 90 phase shifter so that the rotating field may be developed.

In the case of such a tube transmitter, connected in push-pull fashion, it is relatively easy to provide circuits which will take care of maintaining power supply to the bridge automatically in balanced to ground condition.

In the arrangement shown by Fig. 7, the two storage amplifier units, conventionally represented at I00 and I00, are connected to the bridge balance points I8 and I8, respectively, through the input step-up transformers represented at 21 and 21 with a voltage step-up ratio of about to 1.

As in the arrangements previously disclosed and described, the plate energy supply for the various tubes of the storage amplifier units is provided from the sam generator or oscillator IIO which supplies the energy to the field coils. Such energy may, as already stated, be developed at a 13 frequency of the order of 10 to 30 kc., with a line voltage applied to the tubes of the separate storage amplifier units being of the order of 100 volts.

In the arrangement of Fig. 7, the storage amplifier uints I and I00 are shown to include only two stages each, but it will be appreciated that, in practice, six to eight stages are usually to be preferred in order that a stable gain of the order of several hundred thousand may be obtained. The manner of connection of the several additional stages is indicated by Fig. 6 and also by reference to the hereinabove mentioned companion application.

In order to provid the panoramic indication, the cathode ray tube I55 is connected in such a way that its deflecting electrode members I33 and I3I, for instance, are supplied with rectified D. C. energy from the output of the storage amplifier units I00 and I00, respectively. This provides two perpendicular deflection fields within the tube and it will be appreciated, of course, that the deflecting electrodes actually are positioned more nearly in the neck of the tube than shown, and also that these deflectors may, where desired, be of the magnetic variety.

Since the amplifiers I00 and I00 are to provide a direct current output only to energize the deflecting electrode members I33 and I3I, it may, under some circumstances, be desirable to provide additional filtering in the connecting lines I36 and I38, although, generally speaking, the condenser elements of the last storage circuit, conventionally represented at 4| and M, are such that no kc. ripple (this being the assumed frequency of the source H0) can be transmitted to the deflecting elements of the cathode ray tube.

It will be noted, in the connection of Fig. 7, that the deflecting electrode members I32 and I34, arranged in co-operative relationship to the deflecting plate members I3I and I33, respectively. are connected together and connected to a ground which may be the point 25 or its equivalent in the form of the connection to the shield I05. In this Way. with a direct current voltage applied to the deflecting plate electrode members I33 and I 3|, the cathode ray beam I60 would be shifted into one of the four quadrants of the viewing target in accordance with the position of the disturbance and would tend to remain in such a position. However, to obtain a pointer shaped indication, as indicated by Fig. 7, rather than an immobilized spot, the cathode ray tube may be assumed to be energized with A. .C. plate voltage instead of a constant D. C. voltage. To this end, the alternating current energy is supplied at the terminals I52 and then fed through the transformer I54 to energize the various electrode members within the tube. The frequency of the alternating current at the terminal I52 may be anything from the normal 60 cycle supply up to the assumed frequency of the source IIO.

In the example shown by Fig. 7, the tube I55 is assumed to be focused electrostatically and its electron gun I 59 is connected intermediate the cathode I57 and the plate or anode coating through a bleeder resistor I56, so that the spot I60 on the end of the tube remains sharply focused during the complete cycle of operation. With this arrangement. it will be seen that the resulting spot I60 on the tub I55 is in the form of a linear pointer, with its brightest portion at the center of the viewing target and a dim tip pointing in a quadrant in which the located ferro-magnetic body is positioned. In this case,

to the loops lfll to I04,

conditions. However, an extremely accurate representation for one disturbance is obtained, and checks can frequently be made from time to time by the systems heretofore disclosed, to guard against the possibility of false indications. It should be noted, however, in this connection, that the indication of a resultant, rather than individual indications in a group is not a defect, because the farther remote the disturbing objects are located relative to the indicator the less important the individual indication becomes, As an example, if the system should be used to detect submarines, for instance, and a group or pack of submarines were a substantial distance fromthe energy source, the indicator would indicate the correct direction toward the apparent center of the pack or group, which would be a useful and a desirable indication. Then, as the group came nearer or the searcher approached the group, a sharp null indication for each separate disturbance, or, in the assumed case, each separate submarine, would be obtainable once the searching vessel moved over the submarine or very near to it. In order to release a depth charge, such indications would be had at all times, irrespective of whether the disturbing body or submarine was at rest or in motion.

Fig. 8 represents a circuit arrangement for the production of an indicator diagram on the oscilloscope screen I 30 in the form of a narrow pointer I50 which may assume any direction within 360 and the length of which increases, measured from the center outwardly, in proportion to the nearness of a disturbing effect or body Ill.

The arrangement is a form of balanced modulator with a single source of alternating current 2! of any arbitrary frequency, preferably 60 cycles, serving as the power supply frequency of the oscilloscope I30. The circuit comprises two tubes 2! and 202 of the diode-triode type. Under the action of the voltage in the secondary of transformer 2 I0, the triode sections will emit halfwaves of plate current, the amplitude of which is controlled by the D. C. bias which is developed at the last output storage circuits connected to the plates or anodes of the tubes 45 and 45', assumed to be the last two units of storage amplifiers I00 and I00 energized by the two phases of a 2 phase'A. C. voltage source I I0- as in Fig. 7).

In the balanced condition, the half-wave outputs from the triodes 20I and 202 are of an average height and their effect upon the deflectors I32 and I34, respectively, is being cancelled and the cathode ray consequently kept at rest by adjusting the tappirig points in the volume controls I 205, 205, respectively, which derive current through the diode sections within the triode bulbs, and which tapping points connect to 'deflecto-r electrodes ISI and I33.

Under these conditions it is apparent that any deviation of the applied grid-bias above or below the average or balanced value will result in a deflection directed toward or away from the deflectors I32, I34, respectively. Furthermore, this I60 will increase as the defiection will increase in the direction, as indicated, as the unbalance increases in the same sense. The arrangement will, therefore, serve to make indications of both the bearing and the proximity of the object if it is connected to the output of the quadrupole-twin amplifier unit energized by the two-phase current, as was described and explained in the preceding figures.

To improve the reaching distance of the apparatus, multiple field producers, mounted on a plurality of ships or other carriers which are sailing or moving (or even stationary) at substantially uniformly spaced distances from each other comparable to the wave length of the generator source (for instance, six miles for a 30 kc. source) may be provided. In all such uses, the transmitters should be synchronized to each other, both as to frequency and phase, and, under these circumstances, the field energy experiences an increase in certain directions and the field strength pattern becomes directional, as in the case of the multiple dipole antenna rays. The fields may be synchronized by cable or radio and, with the regular pattern arrangement provided, the developed magnetic fields may be caused to penetrate into the water to much greater depths than would otherwise be possible. This will then provide for increasing very substantially the reaching distance of the device in order to detect disturbing conditions such as submarines or wrecks in the water. Thus, the device herein described becomes particularly useful when the disturbing objects come closer to the source of the radiated energy. Thus, it becomes possible to use the arrangement and system hereinabove explained in combination with suitable farreaching ultra-sonic devices.

The arrangement shown particularly by Fig. 4 may be installed on board airplanes or airships (dirigibles) as well. The arrangement, with one single horizontal coil, provides a deflection maximum, if the position of the ferro-magnetic body is just beneath the installation. Since the system operates purely as an inductive bridge and at low input impedance, little trouble is encountered from movements of the crew aboard the ship. Simple electrostatic shielding of the cabin is sufiicient to avoid reactions from movements aboard the ship upon the bridge balance.

Bi-directional indications on board non-metallic planes or blimps may also be obtained. To accomplish this end requires the installation of two vertical coils which are either shielded from each other by metallic coating or by adequate I mutual separation, as hereinbefore suggested, particularly in what was shown by Fig. 5 and its description.

Having described the invention, what is claimed 1. An electron tube circuit comprising a plurality of cascade connected rectifier devices, a source of alternating current for supplying operating voltages for said rectifier devices with alternate tubes of the cascade being connected to be energized in alternate polarity so as to form the cascade into two groups of alternately conductive rectifier devices, an energy storage circuit connected to each rectifier to receive an electrical charge built up in accordance with the output current flow through the individually con- F nected rectifiers, inductive loop means, means for connecting the said source of alternating current to said inductive loop means to develop an electro-magnetic field relative thereto and Within a reaching distance thereof determined by the supply of alternating current, means to initiate a current flow in the first rectifier of the cascade in accordance with the presence of bodies coming within the reaching range of the efiect of the developed electro-magnetic field, a direct connection from the output of each rectifier of the cascade to the input of the next succeedin rectifier to control in sequence the current flow in the rectifiers and the charge stored in the associated storage circuit under the influence of the first stored charge from the first of the rectifiers to the last of the cascade at each halfcycle of the supplied alternating current, and a load circuit connected to receive the energy output of the last rectifier of the cascade sequence.

2. An electron tube circuit comprising a plurality of thermionic elements having the output circuit of one directly connected in cascade to theinput circuit of the following, a source of alternating current for supplying operating voltages for said thermionic elements so that alternate tubes of the cascade are connected to the source in alternate polarity so as to form the cascade into two alternately conductive groups of thermionic elements, an energy storage circuit connected to each of said thermionic elements to receive an electrical charge varied in accordance with the current flowing in the associated thermionic elements, means to bias the first of said thermionic elements to establish a predetermined current flow therethrough during normally conductive periods, means for establishing a direct connection from the output of each thermionic element of the cascade to the next succeeding element to control the current fiow in the several elements in proportion to the charge energy stored in the first of said storage circuits so that an electrical charge is acquired by the last of the storage circuits after sequential steps from one storage circuit to another at each half-cycle of the supplied alternating current, inductive loop means connected to said source of alternating current supply so that an electro-magnetic field extending for a predetermined distance therefrom is developed as a result of current fiow through the said inductive loop means, means including the inductive loop to supply a control voltage to the first thermionic element of the cascade to vary the current flow therethrough. in proportion to the disturbin effects due to transient bodies coming within the reaching area of the developed electro-magnetic field, and a load circuit connected to receive the output from the last of the said thermionic elements.

3. In a locating system wherein there is included a plurality of cascaded directly connected grid-controlled rectifier devices and a source of alternating current for supplying alternating current to the said rectifier devices to provide operating voltages therefor with alternate tubes of the cascade being connected in alternate polarity with the said alternating current source so as to form the cascade into two groups of tubes alternately conductive and wherein each of the tubes is loaded by an energy storage circuit connected in the output circuit thereof, and wherein the said source of alternating current is connected to inductive loop means so as to develop within a predetermined reaching distance thereof an electro-magnetic field of predetermined magnitude, the method of detecting and locating the presence of bodies tending to alter the normally produced field which includes the steps of initiating a normal current flow in the first rectifier of the cascade, charging the storage circuit under the control of the produced current fiow, subsequently energizing the several rectifiers of the cascade in sequence under the control of the stored charge at each half-cycle of the supplied alternating current to charge the respectiveenergy storage circuits, developing an electro-magnetic field of predetermined field strength by the application of the alternating current to the loop, said field having a reaching distance from the inductive loop which is dependent upon the applied alternating current, modifying the current fiow in the first and subsequent rectifiers in accordance with field changes of the developed magnetic field as varied by the presence of ferromagnetic bodies coming within the reaching range of the said field, and controlling a load circuit in accordance with the charge stored in the storage circuit .of the last rectifier of the cascade so that the load circuit current changes are a measure of the chan e from a normally produced electro-magnetic field.

4. An amplifier system comprising a plurality of cascaded directly connected grid-controlled rectifier tubes, a source of alternating current, means for supplying alternating current from the source to the said tubes to provide operating voltages therethrough with alternate tubes of the cascade being connected in alternate polarity with the said alternating current source so as to form the cascade into two groups of alternately conductive tubes, an energy storage circuit comprising parallelly connected resistor and condenser elements having a predetermined time constant connected to the output of each rectifier tube of the cascade, means to supply a predetermined bias voltage upon the cathode circuit of the first tube of the cascade whereby the applied bias is effective throughout the complete cascade, means responsive to a variation in electromagnetic field strengths to initiate a current flow in the first tube of the cascade independently of the applied bias voltage, means for controlling the several rectifier tubes of the cascade in sequence under the influence of the charge from each preceding storage stage to provide a bias voltage for the next succeeding tube at each half-cycle of the supplied alternating current, and a load circuit to indicate the current variations.

5. An amplifier system comprising a plurality of cascaded directly connected rectifier elements, a source of alternating current, means for supplying alternating current from the source to the said rectifiers to provide operating voltages therethrough with alternate rectifiers of the cascade being connected in alternate polarity with the said alternating current source so as to form the cascade into two groups of rectifiers alternately conductive, an energy storage circuit comprising arallelly connected resistor and condenser elements having a time constant at least equal to a time period corresponding to one-half the cycle of the source of alternating current connected to the output of each rectifier of the cascade, electromagnetically activated means to initiate a current flow in the first tube of the cascade, impedance means to supply an alternatingcurrent bias upon the cathode circuit of the first rectiher of the cascade, whereby the applied bias is effective throughout the complete cascade, a load circuit, and means for releasing the effect of the stored charge from each of the storage circuits in sequence to the next direct connected tube to provide a bias voltage thereon at each half-cycle of the supplied alternating current to produce an indication of the controlling electromagnetic effeet on the load circuit.

6. An indicating system comprising a plurality of thermionic tubes connected in series. cascade, an inductive loop element, an alternating current source of energy of predetermined frequency connected to supply operating voltages to the tubes of the said cascade, transformer means connected to receive energy from the source of alternating current and to supply said energy from the secondary terminals thereof to the said loop element to develop a predetermined strength electromagnetic field within a predetermined reaching dis-- tance of the loop, means to bias the said cascade of tubes to establish normally a predetermined current flow therethrough, means to balance the normal loop inductance and to form with transformer secondary winding a balanced bridge circuit, transformer means connected across one diagonal of the formed bridge to the input of the first tube of the plurality of cascaded tubes to apply thereto a control voltage measuring conditions tending tomodify the normally produced electromagnetic field to cause an unbalancing of the said bridge, anda signal indicating circuit connected to receive the output energy from the tube cascade to produce a manifestation of the magnitude and remoteness of alterations of the magnetic field. e

7. An indicating system comprising a plurality of thermionic tubes connected in series cascade, an inductive loop element, an alternating current source of energy of predetermined frequency connected to supply operating Voltages to the tubes of the said cascade, transformer means connected to receive alternating current energy'of like frequency and phase and to supply said ener y from the secondary terminals thereof to the said, loop element to develop a predetermined strength electromagnetic field within a predetermined reaching distance of the loop, means to bias the said cascade of tubes to establish normally a predetermined current flow therethrough, means to balance the normal loop inductance and to form with transformer secondary winding a balanced bridge circuit, transformer means connected across one diagonal of the formed bridge to the input of the first tube of the plurality of cascaded tubes to apply thereto a control voltage measuring conditions tending to modify the normally produced electromagnetic field to cause an unbalancing of the said bridge, and a signal indicatin circuit connected to receive the output energy from the tube cascadeto produce a manifestation of the magnitude and remoteness of alterations of the magnetic field.

8. An indicating system comprising, in comb-i nation, a series cascade of thermionic tubes, a pair of inductive loop elements, and a source of alternating current energy of predetermined frequency connected to supply operating voltages to the tubes of the said cascade and to energize the said loops at like phase and frequency to develop predetermined strength electromagnetic fields within predetermined reaching distances thereof, means to bias the said cascade of tubes to establish normally a predetermined current flow therethrough, a bridge circuit including the said loops for applying a control voltage to modify the normal current flow in the cascade with changes in the sensitivity of the resulting electromagnetic fields causing an unbalance of the bridge, and a signal indicating circuitto produce 19 a manifestation of the magnitude and remoteness of alterations of the magnetic field.

An electrical apparatus comprising a pluraiity of inductive loop elements connected in normally balanced relationship, an electron tube circuit including a plurality of thermionic tubes coni'ieeted series cascade, a source of alternating current, means for supplying operating voltages for said tubes of the cascade from the source of alternating current, a current step-up transformer having its primary winding connected to the alternating current source and its outer secondary winding terminals connected to the said loops for supplying the energy from the alterna currez'it source to the said inductive loop ele nts to develop electromagnetic fields of predetermined magnitude within predetermined reaching distances of the said loops, means operating in phase with the said alternating current for biasing the said tube cascade relative to ground to a predetermined voltage whereat a predetermined normal current flows through the cascade in sequential steps from one to another of the tubes thereof, means responsive to the sensitivity of the said electromagnetic fields to apply a proportional voltage to the input circuit of the first of the tubes of the cascade so that for field conditions tending to alter either of the electromagnetic fields Within the pre-established reaching distance of the loops a proportional current flows in the said tube cascade, and a load circuit connected to receive the energy output of the said cascade and to produce an indication of the magnitude of the departure from equilibrium value of either of the said electromagnetic fields.

10. An electrical apparatus comprising, in combination, a plurality of inductive loop elements connected in normally balanced relationship, an

electron tube circuit including a plurality of thermionic tubes connected in series cascade, and a source of alternating current, means for supplying energy from the source of alternating current to provide the operating voltages for said tubes of the cascade, a current step-up transformer having its primary winding connected to the alternating current source and its outer secondary winding terminals connected to the said loops for supplying the energy from the alternating current source to the said inductive loop elements to develop electromagnetic fields of predetermined magnitude within predetermined reaching distances of the said loops, means for biasing the first tube of the said tube cascade to provide a predetermined. normal current flow therethrough and through the complete cascade, means responsive to changes in the sensitivity of said loops due to the presence of external ferro-magnetic bodies coming within the reaching field thereof to apply a proportional voltage control to the input circuit of the first of the tubes of the cascade so that for field conditions tending to alter either of the electromagnetic fields within the pre-established reaching distance of the loops a proportional current flows in the said tube cascade, and a load circuit connected to receive the energy output of the said cascade and to produce an indication of the magnitude of the departure from equilibrium value of either of the said electromagnetic fields.

11. An electrical apparatus comprising, in combination, an inductive loop element, a signal amplifying circuit including a plurality of thermionic tubes connected in series cascade, a source of alternating current, means for connecting the source of alternating current to provide operating voltages for said cascaded tubes, a current transformer means for supplying energy from the alternating current source to the said inductive loop to develop an electromagnetic field of predetermined magnitude within predetermined reaching distance thereof, capacity means for providing an inductive and capacitive circuit resonant at the frequency of the alternating current source to strengthen the current flow through the said inductance, means for biasing the said tube cascade to a predetermined voltage whereat a predetermined normal current flows through the cascade, means responsive to term-magnetic bodies coming within the said produced field to apply a proportional voltage change upon the cascaded tubes to provide a proportional change in the current fiow through the cascade, and an indicator circuit connected to respond to the energy output of the said cascade so as to indicate the presence of bodies within the reaching range of the effect of the said electromagnetic field. l

12. An electrical apparatus comprising an inductive p element, an electron tube circuit including a plurality of thermionic tubes connected in series cascade with the output of one tube being connected to the input of the succeeding tube of the cascade, a source of alternating current, means for supplying operating voltage for said tubes of the cascade from the source of alternating current, a transformer having its primary winding connected to the alternating current source and its secondary winding connected to the inductive loop for supplying the energy of the alternating current source to the inductive loop element to develop anelectromagnetic field of predetermined magnitude within a predetermined reaching distance of the loop, means to balance the loop to provide an electrical bridge connection of which an intermediate point on the said transformer winding and one loop terminal form the terminal points of a diagonal across which at a normally predetermined equilibrium condition no voltage is developed, a connection from one end of the said diagonal to ground, means for biasing the said tube cascade relative to ground to a predetermined voltage whereat a predetermined normal current flows through the cascade, means for energizing the input circuit of the first of the tubes of the cascade with a voltage corresponding to that at the ungrounded bridge diagonal point so that for field conditions tending to alter the electromagnetic field within the pre-established reaching distance of the loop a voltage to unbalance the bridge diagonal is developed and applied as a signal voltage to the said tube cascade, and a load circuit connected to receive the energy output of the said cascade and to produce an indication of the magnitude of the departure from equilibrium value of the voltage across the said bridge and thereby of the magnitude and distance of the effect modifying the normal electromagnetic field.

13. An indicating system comprising a plurality of directly connected thermionic tubes connected in series cascade to supply the output energy from the several tubes directly to the input of the next succeeding tubes of the cascade, energy storage means connected to receive the output energy from each tube of the cascade so that the magnitude of accumulated charge is proportional to the current flowing in the associated tube, an inductive loop element, an alternating current source of energy of predetermined frequency connected to supply voltages to the tubes of the said cascade in such manner that cyclically alternate tubes of the cascade are simultaneously energized by the said source and the other alternate tubes of the cascade are simultaneously de-energized so that'the stored charges bias in sequence the operative tubes, transformer means connected to receive energy from the source of A. C. and to supply said energy from the secondary terminals thereof to the said loop element to develop a predetermined strength electromagnetic field within a predetermined reaching distance of the loop, means to bias the first of the said cascade connected tubes to establish normally a predetermined current flow through the cascade, inductive and resistance means of values substantially equal to the normal loop inductance and resistance connected serially with the loop and transformer secondary winding to form a bridge circuit, connections between the said loop and a predetermined point on the transformer to a plane of normally fixed potential to provide one balanced diagonal loop bridge connection, step-up transformer means connecting said diagonal of the formed bridge to the input of the first tube of the plurality so that for conditions of equilibrium the said applied bias potential alone controls the current flow in the said cascade and for external conditions tending to modify the normally produced electromagnetic field to cause an unbalancing of the said bridge a control voltage is applied to the said amplifier from the said transformer connection, and a signal utilization circuit connected to receive the output energy from the amplifier.

14. An electrical apparatus comprising an inductive loop element, an electron tube circuit including a plurality of thermionic tubes connected in series cascade with the output of one tube being connected to the input of the succeeding tube of the cascade, energy storage circuits connected with each tube of the cascade and arranged to be charged in accordance with the current flowing in the associated tube, a source of alternating current, means for connecting said tubes of the cascade alternately to the source of alternating current in a polarity such that the plurality of tubes of the cascade is divided into two alternatel operative groups, a transformer having its primary winding connected to the alternating current source and its secondary winding connected to the inductive loop for supplying the energy of the alternating current source to the inductive loop element to develop an electromagnetic field of predetermined magnitude within a predetermined reaching distance of the loop, a resistance and a shielded inductance element connected serially with the transformer secondary winding to balance the loop inductance and resistance and to provide an electrical bridge connection of which an intermediate point on the said transformer winding and one loop terminal form the terminal points of a diagonal across which at a normal predetermined equilibrium condition no voltage is developed, a connection from one point on said diagonal to ground, means for biasing the said tube cascade relative to ground to a predetermined voltage whereat a predetermined normal current flows through the cascade in sequential steps from one to another of the tubes thereof, voltage step-up transformer means connecting the input circuit of the'first of the tubes of the cascade and the ungrounded 22 bridge diagonal point so that for field conditions tending to alter the electromagnetic field within the pre-established reaching distance of the loop a voltage to unbalance the bridge diagonal. is developed and applied as a signal voltage to the said tube cascade, and a load circuit connected to receive the energy output of the said cascade and to produce an indication of the magnitude of the departure from equilibrium value'of the voltage across the said bridge and thereby of the magnitude and remoteness of the effect modifying the normal electromagnetic field.

15. An electrical apparatus comprising a plu-o rality of inductive loop elements connected in series, an electron tube circuit including a plurality of series cascaded thermionic tubes, an energy storage circuit connected with each tube of the cascade and arranged to be charged under the control of the current flowing in the associated .tube, a source of alternating current,

means for connecting said tubes of the cascade alternately to the source of alternating current in a polarity such that the plurality of tubes of the cascade is divided into two alternately operative groups, a transformer having its primary. winding connected to be energized by alternating current energy source and its outer secondary connected to the end terminals of the series loops 7 for supplying the energy'of the alternating current source to the inductive loop element to develop an electromagnetic field of predetermined magnitude within a predetermined reaching distance of the loop, serially connected capacity elements connected with the said loop elements to tune said loops to the generator frequency, means for biasing the said tube cascade relative to ground to a predetermined voltage whereat a predetermined normal current flows through the cascade in sequential steps from one toanother of the tubes thereof, voltage step-up transformer means for supplying an energizing control voltage to the input circuit of the first of the tubes of the cascade representative of field conditions tending to alter the electromagnetic field within the pre-established reaching distance of any loop of the plurality so that the amplifier current flow varies from the pre-established normal, depending upon which electromagnetic field is modified, and a load circuit connected to receive the energy output of the said cascade and to produce an indication of the magnitude of the departure from equilibrium value of the said altered electromagnetic field.

6. A locating device comprising, in combination, a plurality of inductive loop elements quadrantally positioned, a plurality of thermionic amplifier devices, and a two-phase alternating current source of predetermined frequency, means for supplying operating energy to each of the said amplifiersifrom difi'erent phases of the said alternating current source, means for connecting diametrically opposite loop'elements of the quadrantal arrangement, means for supplying energy from the said source of alternating current to the said connected pairs of loops with one phase of the alternating current source being supplied to one oppositely connected pair of loops and the other phase being supplied to the other oppositely connected loop pair to generate from the said loops electromagnetic fields of predetermined magnitude extending into each quadrant, means for normally producing a predetermined current flow through each of the said amplifiers, a connection from the connected series of said loop elements to that amplifier device which is energized by a like'phase of the said alternating current source so that external conditions tending. to change the magnetic field distribution produce a control voltage of proportional magnitude to modify the normal current flowing in the con.- nected amplifier, and an indicator circuit to indicate the relative change in current flow in each of the amplifiers simultaneously.

l7. The electrical apparatus claimed in claim 16 comprising, in addition, voltage step-up transformer means to supply the control voltages from the said loops to the said amplifiers.

18. The circuit claimed in claim 16- wherein the said indicator circuit includes a cathode ray tube.

19. A detector circuit for detecting the presence of electromagnetically active bodies which comprises a plurality of inductive loop elements positioned in quadrantal relationship relative to each other and connected serially to each other in diametrically opposing relationship, an amplifier circuit connected to each pair of connected diametrically opposite loop elements, and a twophase source of alternating current energy haying one phase connected to energize one amplifier and the loops connected thereto, and the second phase connected to energize the other or" said amplifiers and the loops connected thereto, whereby an electromagnetic field is developed in the region of each loop element so as to provide a field distribution extending substantially in all quadrants, capacity means included in the connecting path between the said alternating current energy source and each of the said loops to tune the said loop elements to the frequency of the said alternating current source so as to intensify the field strength developed thereby, bias means to control each of the amplifiers to produce a predetermined normal current flow therethrough, means responsive to the presence of disturbing electromagiretically active bodies Within the reaching distances of the fields developed from said loops to produce proportional variances of the current flow in the said amplifiers, and a directionally responsive indicator circuit connected to receive the combined output energy from the said amplifiers to indicate the variance of the magnetic field due to the said disturbing bodies.

20'. The circuit claimed in claim 19 comprising, in addition, a cathode ray indicating device included in the indicator circuit, and means to supply energy from the said alternating current source to said cathode ray tube to provide operating voltages therefor.

21. [-111 indicating system comprising a plurality of inductive loop elements, an amplifier comprising a plurality of cascade connected thermionic tubes, and means to supply alternating current energy to all of said loop elements and the tubes of said amplifier respectively, so as to develop electromagnetic fields of predetermined strength from said loop elements and to cause said amplifier to become operative during positive halfcycles of the alternating current, each of the said supplies being co-phasal and of like frequency, means normally to provide a current fiow of predetermined magnitude in said amplifier during conductive periods thereof, means for supplying control energy to said amplifier to vary the current flow therethrough under the control of external conditions tending to alter the magnetic field sensitivity within the region of any of the developed electromagnetic fields from said loops, and an indicating means to produce indications of the said modifications in amplifier output energy.

22. The system claimed in claim 21 wherein the indicating circuit comprises a cathode ray tube having a pair of electron beam deflecting means for deflecting the developed cathode ray beam in each of two mutually perpendicular directions, an

electron tube having its output circuit connected to each of said deflecting means, means for supplying alternating current energy to said tubes to cause saidtubes to become conductive, said tubes being energized by the saidalternating current during opposite half-cycles in each direction of deflection, and means responsive to the output energy from the said amplifiers to control the deflection of the saidbeam.

23.. A detector circuit for detecting the presence of. disturbing conditions coming within developed electromagnetic fields which comprises a plurality of inductive loop elements positioned in quadrantal relationship relative to each other with diametrically opposite loops connected serially with respect to each other, an amplifier having its input circuit connected to be energized from the connected pair of diametrically opposite loop elements, and a source of two-phase alternating current energy having one phase connected to energize one of said amplifiers and the loops. connected thereto, and the second phase connected to energize the other of said amplifiers and the loops connected thereto, whereby an electromagnetic field is developed in the region of each loop element so as to provide a field distribution extending substantially in all quadrants and the amplifiers become operative under the influence of the alternating current source, impedance means to bias each of said amplifiers to produce a predetermined normal current flow therein, means responsive to the presence of disturbing electromagnetically active bodies within the,

reaching distance of the electrical fields developed by said alternating current energized loops to produce a variance of the current flow in the said amplifiers, and a directionally responsive indicator circuit connected to receive the combined output ener y from the said amplifiers to indicate the quadrant wherein any variance of the magnetic field is produced due to the said disturbing bodies.

24. The circuit claimed in claim 23 comprising, in addition, a cathode ray indicating device included in the indicator circuit to provide the quadrantal indications, means to supply energy from the said alternating current source to said cathode ray tube to provide operating voltages therefor, and means to control the beam deflection within the said cathode ray tube in each of two mutually perpendicular directions in accordance with the output energy from the said amplifiers.

25. A detector circuit for detecting the presence of di 'rbing conditions coming within developed ole rornagnetic fields which comprises a plurality of inductive loop elements positioned in quadrantal relationship relative to each other with diametrically opposite loops connected serially with respect to each other, an amplifier circuit having its input connected to be energized from the connected pair of diametrically opposite loop elements, and a source of two-phase alternating current energy having one phase connected to energize one amplifier and the said loops connected thereto, and the second phase connected to energize the other of aid amplifiers and the loops connected thereto, whereby from the loops an electromagnetic field is developed in the region of each loop element so as to provide a field distribution extending substantially in all quadrants and the amplifiers become operative under the influence of the alternating current energy source, capacity means included in the connecting path between the said alternating current energy source and the said loops to tune the said loop elements to the frequency of the said alternating current source whereby the field strength developed is intensified, means to bias each of the amplifiers to produce a predetermined normal current flow through the said amplifiers, means responsive to the presence of disturbing electromagnetically active bodies within the reaching distance of the electromagnetic fields developed by said alternating current energized loops to produce an increase or a decrease of the current flow in the said associated amplifier in accordance with the location of the disturbance relative to one 01' the other of the connected diametrically opposite loops, and the degree of increase or decrease of current being determined by the nearness or remoteness of the disturbances relative to the loop, and a directionally responsive indicator circuit connected to receive the combined output energy from the said amplifiers to indicate both the magnitude and quadrantal location of any variance of the magnetic field due to the said bodies.

26. The circuit claimed in claim 25 comprising, in addition, a cathode ray indicating device having means to deflect and control the produced cathode ray in mutually perpendicular directions included in the indicator circuit to provide the quadrantal indications of disturbance location, means to supply energy from the said alternating current source to said cathode ray tube to provide operating voltages therefor, means to connect the output of one of the amplifiers to control the deflection of the cathode ray beam in one direction, and means to connect the output of the other of said amplifiers to control the deflection of the cathode ray beam in the second normally perpendicular direction so that the combined efiect is a quadrantally positioned electron beam representative of and pointing in the quadrantal direction of the center of the disturbance.

27. An indicating system comprising, in combination, a series cascade of thermionic tubes, a pair of inductive loop elements, and a source of alternating current energy of predetermined frequency connected to supply operating voltages to the tubes of the said cascade and to energize the said loop at like phase and frequency to develop predetermined strength electromagnetic fields extending to predetermined reaching distances thereof, means to bia the said cascade of tubes to establish normally a predetermined current flow therethrough, capacity means connected with each inductive loop element to tune said elements to the frequency of the energizing alternating current source, a bridge circuit including the said loops for applying a control voltage to modify the normal current flow in the cascade upon the presence of field disturbing conditions modifying the said produced electromagnetic fields and causing an unbalance of the bridge, ferro-magnetic mean for shielding the said tube cascade from the direct efiects of field disturbing conditions which afiect the said loop elements, and a signal indicator circuit to produce a manifestation of the magnitude and remoteness of the external disturbance affecting the said produced magnetic fields.

28. The circuit claimed in claim 2'7 wherein the said indicator circuit includes a cathode ray tube having means therein to develop a cathode ray beam, means associated with the cathode raytube for deflecting the produced cathode ray beam developed therein into each quadrant, means for controlling the said deflection by the said amplifier outputs thereby to indicate, by direction of deflection, that quadrant wherein magnetic field disturbances have occurred and by the magnitude of the deflection the relative nearness of the disturbance.

29. The apparatus claimed in claim 27 wherein the indicator circuit includes a cathode ray tube having means therein for developing an electron beam adapted to impact the tube target to produce visible indications, a plurality of opposing pairs of electron beam deflecting means for defiecting the developed cathode ray beam in mutually normal direction one to the other, means for controlling the deflection in the said two normal directions independently of one another by the output energy from the said amplifiers, rectifier means connected to be energized by alternate half-cycles of the said alternating current energy source, and means for supplying the rectifier output individually to one electron beam deflecting means of each pair for controlling the beam motion in the same plane as the amplifier connected with the same phase of the alternating current source.

KURT SCI-ILESINGER. 

